I read quite a few chapters so I can be very specific, still, I can't for the life of me find this story and I'd really like to finish it. It was amazing! Although somehow very unknown.
The whole story is available as a series of webpages. White site. Thin blocks of text centered. Every page starts with a bigger chapter title at the top.
The story is told from 1st person, of a mind researcher. His company is working on uploading minds. They do this by injecting chemicals that suspend the brain and then stimulating aggressively and recording responses to map the mind. I forget why but he decides to upload his own mind. The story gets weird, the guy starts losing memories, his friends prank him making him think he's in a simulation but he's not yet.
Beyond this point massive spoilers, consider looking if somebody already produced an accepted answer and consider reading this fabulous story yourself instead.
Then things get much weirder and he wakes up in a tiny village where people are normal but life is extremely limited. Medieval-like. There's a literal wall, border, dome, surrounding their habitat they can ride up to with horses (bit far away), but seems impenetrable. The church produces food out of nowhere. The protagonist seems to have special abilities in this world. He doesn't need to breathe or eat although he feels the need. He can also accelerate or slow his perception of time.
Even bigger spoilers, it turns out most of the planet has been converting to a mechanic, very active machine. His dreams, split mind experiences in what seemed like a simulation appear to be memories from his early uploaded mind before it split off and became a super intelligence taking over the planet. The small vestige he lives in turns out to be the intelligence preserving human life from the old world. He manages to break out, things became super interesting, I refuse to spoil things though and doubt it would help finding the story much anyway.
edit: was convinced to add more details.
He spots a weird irregular looking machine one day that the dome opened its wall for somehow. It's globular I vaguely recall with many appendages and leaves no trace where it walks through chaotic multitudinous footsteps. He manages to break out of the dome and ends up in a type of maintenance area where he sees the creature again. Creature takes him to the surface. The entire surface is covered in drains. There is constant rain, everything seems to be efficiently captured. There is no visible life save for many space elevators in the distance. On the surface he can communicate as-if telepathically with a large entity that gives him what seems to be vision from many high-powered satellites above and he finds out the entire planet has been converted and governed and their little dome village is just a tiny blob in the bowels of the planet. He almost gets eaten / cleaned up by some being that arrives although the being appears to intend no harm. He runs, escapes, and that is as far as I read.